Apparatus for Sensor with Programmable Gain and Dynamic Range and Associated Methods

ABSTRACT

An apparatus includes a coil suspended in a magnetic field and an optical detector to detect displacement of the coil in response to a stimulus. The apparatus further includes a feedback circuit to program a gain of the sensor, wherein the feedback circuit is coupled to the optical detector and to the coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to the following patent applications:

U.S. patent application Ser. No. ______, filed on ______, titled“Apparatus for Sensor with Configurable Coil Constant and AssociatedMethods,” Attorney Docket No. SIAU003;

U.S. patent application Ser. No. ______, filed on ______, titled“Apparatus for Sensor with Communication Port for Configuring SensorCharacteristics and Associated Methods,” Attorney Docket No. SIAU004;

U.S. patent application Ser. No. ______, filed on ______, titled“Apparatus for Sensor with Improved Power Consumption and AssociatedMethods,” Attorney Docket No. SIAU005;

U.S. patent application Ser. No. ______, filed on ______, titled“Apparatus for Sensor with Configurable Coil and Associated Methods,”Attorney Docket No. SIAU006;

U.S. patent application Ser. No. ______, filed on ______, titled“Apparatus for Sensor with Configurable Damping and Associated Methods,”Attorney Docket No. SIAU007; and

International Application No. PCT/US2013/032584, filed on Mar. 15, 2013,titled “Closed Loop Control Techniques for Displacement Sensors withOptical Readout.” The foregoing applications are incorporated byreference in their entireties for all purposes.

Furthermore, the present patent application is a continuation-in-part ofInternational Application No. PCT/US2013/032584, filed on Mar. 15, 2013,titled “Closed Loop Control Techniques for Displacement Sensors withOptical Readout,” which claims priority to: (1) Provisional U.S. PatentApplication No. 61/712,652, filed on Oct. 11, 2012; and (2) ProvisionalU.S. Patent Application No. 61/721,903, filed on Nov. 2, 2012. Theforegoing applications are incorporated by reference in their entiretiesfor all purposes.

TECHNICAL FIELD

The disclosure relates generally to sensors, such as acceleration,speed, and displacement sensors and, more particularly, to apparatus forsuch sensors with programmable gain and dynamic range, and associatedmethods.

BACKGROUND

With advances in electronics, a variety of sensors have been developedto sense physical quantities. The sensors may use a variety oftechnologies, such as electrical, mechanical, optical, andmicro-electromechanical systems (MEMS), or combinations of suchtechnologies. More particularly, some sensors can sense displacement,velocity, or acceleration. Sensors that can sense displacement,velocity, or acceleration find use in a variety of fields, such asground or earth exploration, for instance, reflection seismology.

As an example, devices known as geophones use a magnet and a coil thatmove relative to each other in response to ground movement. Waves sentinto the earth generate reflected energy waves. In response to reflectedenergy waves, geophones generate electrical signals that may be used tolocate underground objects, such as natural resources.

FIG. 1 illustrates a conceptual diagram 10 of a geophone, which includesa magnet 16 coupled to an anchor point 12 (e.g., housing) and spring 14,and coil 18 with mass m. In response to a stimulus, such as the energywaves described above, coil 18 moves in relation to magnet 16. As aresult, an electrical output signal is generated by coil 18.

The coil-spring assembly form a physical system that respondsnon-uniformly as the frequency of the stimulus is varied. Assuming thatspring 14 has a spring constant k, the coil-spring assembly, with mass m(i.e., a negligible spring mass), has a natural frequency of oscillationof

$f_{N} = {\sqrt{\frac{k}{m}}.}$

FIG. 2 illustrates a frequency response curve 20 of the geophone of FIG.1 to physical stimuli. Frequency response curve 20 has a peak 23 at thefrequency f_(N). Thus, geophone 10 has better response (higher outputsignal level) at frequencies near or equal to f_(N).

Note that the description in this section and the corresponding figuresare included as background information material. The materials in thissection should not be considered as an admission that such materialsconstitute prior art to the present patent application.

SUMMARY

According to one exemplary embodiment, an apparatus includes a coilsuspended in a magnetic field and an optical detector to detectdisplacement of the coil in response to a stimulus. The apparatusfurther includes a feedback circuit to program a gain of the sensor,wherein the feedback circuit is coupled to the optical detector and tothe coil.

According to another exemplary embodiment, a method is disclosed foroperating a sensor. The sensor includes a coil suspended in a magneticfield and an optical detector to detect displacement of the coil inresponse to a stimulus. The method includes programming a gain of thesensor by using a feedback circuit that is coupled to the opticaldetector and to the coil.

According to another exemplary embodiment, a sensor includes a magnet,having an associated magnetic field; a coil suspended by a spring in themagnetic field of the magnet; and an optical detector to detectdisplacement of the coil in response to a stimulus applied to thesensor. The sensor further includes a feedback circuit coupled to theoptical detector and to the coil, the feedback circuit to program a gainof the sensor by using at least one nonlinear transfer function.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings illustrate only exemplary embodiments andtherefore should not be considered as limiting the scope of theapplication or the claims. Persons of ordinary skill in the artappreciate that the disclosed concepts lend themselves to other equallyeffective embodiments. In the drawings, the same numeral designatorsused in more than one drawing denote the same, similar, or equivalentfunctionality, components, or blocks.

FIG. 1 illustrates a conceptual diagram of a geophone.

FIG. 2 depicts the frequency response of a geophone in response tophysical stimuli.

FIG. 3 shows a sensor according to an exemplary embodiment.

FIG. 4 depicts forces operating in a sensor according to an exemplaryembodiment.

FIG. 5 illustrates a virtual spring caused by use of negative feedbackin an exemplary embodiment.

FIG. 6 depicts a cross-section of a sensor according to an exemplaryembodiment.

FIG. 7 illustrates a cross-section of a sensor according to an exemplaryembodiment.

FIG. 8 shows a schematic diagram of a sensor according to an exemplaryembodiment.

FIG. 9 illustrates a schematic diagram of a sensor according to anexemplary embodiment.

FIG. 10 depicts an output signal of a trans-impedance amplifier (TIA) inan exemplary embodiment.

FIG. 11 shows a flow diagram for a method of operating a sensoraccording to an exemplary embodiment.

FIG. 12 illustrates a block diagram of a sensor communicating withanother device or component according to an exemplary embodiment.

FIG. 13 depicts a nonlinear transfer function used to modify the gainand dynamic range of a sensor according to an exemplary embodiment.

FIG. 14 shows a nonlinear transfer function used to modify the gain anddynamic range of a sensor according to another exemplary embodiment.

FIG. 15 illustrates a number of nonlinear transfer functions that may beused in a sensor according to an exemplary embodiment.

FIG. 16 depicts a block diagram of a circuit arrangement for a sensorhaving programmable gain and dynamic range according to an exemplaryembodiment.

FIGS. 17-18 show circuit arrangements that may be used for programming afeedback network of a sensor according to an exemplary embodiment.

DETAILED DESCRIPTION

The disclosed concepts relate generally to sensors, such asacceleration, speed, and displacement sensors. More specifically, thedisclosed concepts provide systems, apparatus, and methods for sensorswith programmable gain and dynamic range/dynamic range compression.

Sensors according to exemplary embodiments can sense acceleration,velocity, and/or displacement. As persons of ordinary skill in the artunderstand, acceleration, velocity, and displacement are governed bymathematical relationships. Thus, one may sense one of acceleration,velocity, and displacement, and derive the others from it.

For example, if acceleration, a, is sensed, velocity, v, anddisplacement, x, may be derived from a. More specifically:

$a = {\left. \frac{v}{t}\Rightarrow v \right. = {\int{a \cdot {t}}}}$$v = {\left. \frac{x}{t}\Rightarrow x \right. = {\int{v \cdot {t}}}}$

Sensors according to exemplary embodiments include a combination ofelectrical, optical, and mechanical components. FIG. 3 illustrates aconceptual diagram of a sensor 100 according to an exemplary embodiment.

Referring to FIG. 3, sensor 100 includes a spring 106 attached (e.g., atone end) to an acceleration reference frame or plane 103. Spring 106 hasa spring constant k_(s). Spring 106 is also attached (e.g., at anotherend) to coil 109. Coil 109 and its corresponding assembly (not shown),e.g., a bobbin, have a mass m, also known as proof mass.

A magnet 112 is positioned near or proximately to coil 109. A magneticfield 112A is established between the north and south poles of magnet112. Thus, coil 109 is completely or partially suspended within magneticfield 112A. By virtue of spring 106, coil 109 may move in relation tomagnet 112 and, thus, in relation to magnetic field 112A.

More specifically, in response to a physical stimuli, such as a forcethat causes displacement x of coil 109, coil 109 moves in relation tomagnet 112 and magnetic field 112A. As persons of ordinary skill in theart understand, movement of a conductor, such as coil 109, in a magneticfield, such as magnetic field 112A, induces a current in the coil. Thus,in response to the stimuli, coil 109 produces a current.

Optical position sensor 115 detects the movement of coil 109 in responseto the stimuli. More specifically, as described below in detail, opticalposition sensor 115 generates an output signal, for example, a current,in response to the movement of coil 109.

Note that in some embodiments, rather than generating a current, opticalposition sensor 115 may generate a voltage signal. For example, opticalposition sensor 115 may include a mechanism, such as an amplifier orconverter, to convert a current produced by the electro-opticalcomponents of optical position sensor 115 to an output voltage. Ineither case, optical position sensor 115 provides an output signal 115-1to amplifier 118.

Without loss of generality, in exemplary embodiments, amplifier 118constitutes a TIA. TIA 118 generates an output voltage in response to aninput current. Thus, in the case where optical position sensor 115provides an output current (rather than an output voltage) 115-1, TIA118 converts the current to a voltage signal.

In some embodiments, depending on a number of factors, TIA 118 mayinclude circuitry for driving coil 109, such as a coil driver (notshown). Such factors include design and performance specifications for agiven implementation, for example, the amount of drive specified forcoil 109, etc., as persons of ordinary skill in the art will understand.

TIA 118 (or other amplifier circuitry, as noted above) provides anoutput signal 118-1 to coil 109. The polarity of output signal 118-1 isselected such that output signal 118-1 counteracts the current inducedin coil 109 in response to the physical stimuli. In other words, opticalposition sensor 115 and TIA 118 couple to coil 109 so as to form anegative-feedback loop or circuit.

The feedback or driving signal, i.e., signal 118-1, causes a force toact on coil 109. In exemplary embodiments, the force is proportional tothe displacement x. Thus, a force exerted by spring 106 and a forceexerted by coil 109 (by virtue of negative feedback and driving signal118-1) cooperate with each other against the force created byacceleration of coil 109 (the proof mass). FIG. 4 illustrates the twoforces.

More specifically, FIG. 4 shows a force vector 121 that corresponds toforce F_(s) exerted by spring 106. FIG. 4 also depicts a force vector124 that corresponds to force F_(c). exerted by virtue of theacceleration of coil 109. According to Hook's law, force F_(s) relatesto displacement x, specifically F_(s)=−k_(s)·x, where, as noted above,k_(s) represents the spring constant of spring 106. In effect, spring106 resists the displacement in proportion to k_(s).

Furthermore, according to Newton's second law (ignoring any relativisticeffects), force F_(c) relates to the mass of coil 109 (including anyphysical components, such as a bobbin), and to the acceleration thatcoil 109 experiences as a result of the external stimuli (e.g., thesource that causes displacement x to occur). Specifically,F_(c)=m_(c)·a, where m_(c) represents the mass of coil 109, and adenotes the acceleration that coil 109 experiences.

As noted above, negative feedback is employed in sensor 100 (see FIG. 5)so as to cause the mass m_(c) to come to equilibrium. Mathematicallystated, the feedback causes the mass m_(c) to come to equilibrium whenF_(s) equals F_(c). Thus, sensor 100 may be viewed as operatingaccording to a force-balance principle, i.e., F_(s)=F_(c) atequilibrium.

Stated another way, force-balance occurs when −k_(s)·x=m_(c)·a. One mayreadily determine the spring constant k_(s) and the mass of coil 109,m_(c) (e.g., by consulting data sheets or controlling manufacturingprocesses, etc.). Using the values of k_(s) and m_(c) in the aboveequation, one may determine the acceleration of coil 109 in response tothe stimulus, i.e.:

$a = {\frac{{- k_{s}} \cdot x}{m_{c}}.}$

In other words, output signal 118-1 of TIA 118 is proportional toacceleration a. Given acceleration a, velocity v, and displacement x maybe determined, by using the mathematical relations described above.(Note also that optical position sensor 115 may also determinedisplacement x). Thus, sensor 100 may be used to determine displacement(position), velocity, and/or acceleration, as desired.

Using negative feedback provides a number of benefits. First, itflattens or tends to flatten the response of sensor 100 to the stimuli.Second, feedback increases the frequency response of sensor 100, i.e.,sensor 100 has more of a broadband response because of the use offeedback.

Third, negative feedback reduces the amount of displacement that resultsin a desired output signal level. In effect, negative feedback acts as avirtual spring coupled in parallel with spring 106, a concept that FIG.5 illustrates. More specifically, the negative-feedback signal appliedto coil 109 causes virtual spring 130 to counteract force F_(c), whichis exerted because of the acceleration of coil 109, as described above.Thus, spring 106 and virtual spring 130 work as additive forces to reachforce equilibrium in opposition to the force created by acceleration ofthe coil mass (proof mass). Virtual spring 130 is controlledelectronically, e.g., by TIA 118 in FIG. 3.

Referring again to FIG. 5, because of the use of negative feedback,virtual spring 130 has a larger spring constant, k_(v), than does spring106. Use of virtual spring 130 results in sensor 100 creating a givenoutput in response to a smaller stimulus. Put another way, virtualspring 130 acts as a stiff spring. Thus, compared to an open-looparrangement, sensor 100 has a reduced total displacement for a desiredlevel of output signal. Also, force applied to a sensor that uses anopen-loop arrangement (e.g., a geophone), causes the mass suspended bythe spring to wobble more, which limits the upper response limit of thesensor.

As noted, use of negative feedback flattens or tends to flatten thesensor frequency response, and also reduces the sensitivity of theforce-balance system to the value of spring constant k_(s) of spring106, since the spring constant of virtual spring 130 dominates. Abenefit of the foregoing is to allow the use of a stiffer springsuspension 106, which in turn facilitates sensor operation at anyorientation with respect to Earth's gravity. Additionally, an increasein loop gain results in a stiffer virtual spring constant 130, which inturn allows a larger full scale stimulus range.

Note that a variety of embodiments of sensors according to thedisclosure are contemplated. For example, in some embodiments, theposition of coil 109 and magnet 112 may be reversed or switched (seeFIG. 3). Thus, coil 109 may be stationary, while magnet 112 may besuspended by spring 106.

As another example, in some embodiments, more than one magnet 112 may beused, as desired. As yet another example, in some embodiments, more thanone coil 109 may be used, e.g., two coils in parallel or series, asdesired. Other arrangements are possible, depending on factors such asdesign and performance specifications, cost, available technology, etc.,as persons of ordinary skill in the art will understand.

FIG. 6 depicts a cross-section of a sensor 200 according to an exemplaryembodiment. Sensor 200 includes a housing, frame, or enclosure 205 toprovide physical support for various components of sensor 200. In theembodiment shown, housing 205 has sides 205A, 205B, 205C, and 205D, forexample, a top, a right side or wall, a bottom, and a left side or wall.Other housing, frames, or enclosures are possible and contemplated, aspersons of ordinary skill in the art will understand.

Magnet 112 is arranged with magnet caps 215A and 215B. In the embodimentshown, magnet 112 is disposed between magnet caps 215A and 215B. Avariety of types and shapes of magnets may be used, as desired. Examplesinclude neodymium-iron-boron (NIB) or aluminum nickel cobalt (ALNICO)alloy magnets, but other materials, such as alloys with appropriateproperties, may be used. Other arrangements of the magnet and magnetcaps or support are possible and contemplated, as persons of ordinaryskill in the art will understand.

Coil 109 is wound on a bobbin 220. In the embodiment shown, coil 109 andbobbin 220 together form the proof mass (neglecting the mass of spring106). In the embodiment shown, coil 109 is wound in two sections onbobbin 220, although other arrangements are possible and contemplated,as persons of ordinary skill in the art will understand.

The proof mass is suspended by spring 106, which for illustrationpurposes is shown as four sections labeled 106A-106D. In exemplaryembodiments, spring 106 may include one, two, or more springs, such asflat, leaf, or spider springs, as desired. Other types and/orarrangements of spring 106 are possible and contemplated, as persons ofordinary skill in the art will understand. A variety of materials andtechniques may be used to fabricate spring 106. Some examples includeetching or die cutting. Beryllium copper may be used as one example ofspring material, but other materials with appropriate spring properties(e.g., having relatively low temperature coefficient) may be used, asdesired.

In exemplary embodiments, such as the embodiment of FIG. 6, spring 106may have a relatively low spring constant. More specifically, spring 106may have sufficient stiffness to suspend and support the proof mass. Asnoted above, a virtual spring (not shown) having a relatively highspring constant (i.e., higher than the spring constant of spring 106)operates in conjunction with spring 106. Thus, spring 106 may providejust enough stiffness to physically support the proof mass.

In the embodiment shown in FIG. 6, spring 106 (shown as sections orportions 106A-106D) suspend the proof mass with respect to magnet 112(and magnet caps 215A-215B, if used). In other words, a stimulus, suchas force, applied to sensor 200 causes the proof mass to move orexperience a displacement with respect to magnet 112 (and magnet caps215A-215B). Other arrangements are possible and contemplated, as personsof ordinary skill in the art will understand. For example, spring 106may attach to housing 205, rather than magnet caps 215A-215B.

Sensor 200 includes an optical interferometer to generate an electricalsignal in response to displacement of coil 109 in relation to magnet 112or housing 205. The electrical signal constitutes the output of theoptical interferometer. The electrical signal may be provided to anamplifier, e.g., TIA 118 in FIG. 3.

Referring again to FIG. 6, in the embodiment shown, the opticalinterferometer includes a light source 225, such as a vertical cavitysurface-emitting laser (VCSEL). The light output of light source 225 isreflected by a minor 222, and is diffracted by diffraction grating 235.The resulting optical signals are detected by optical detectors 230A,230B, and 230C.

A mechanical or physical stimulus applied to sensor 200 causes a changein the detected light, and thus causes optical detectors 230A-230C toprovide an electrical output signal. The electrical output signal, e.g.,a current signal, may be used in a feedback loop, as discussed above.

Note that, if desired, the electrical output signal may be used in anopen-loop configuration, rather than in a closed-loop (negativefeedback) configuration. As noted above, closed-loop configurationprovides some advantages over open-loop configuration. In somesituations, however, operating sensor 200 in an open-loop configurationmay be desired, for instance, on a temporary basis.

FIG. 7 depicts a cross-section of a sensor 250 according to an exemplaryembodiment. Sensor 250 includes a housing, frame, or enclosure 205 toprovide physical support for various components of sensor 250. In theembodiment shown, housing 205 has sides 205A, 205B and 205C, forexample, a right side or wall, a bottom, and a left side or wall. Otherhousing, frames, or enclosures are possible and contemplated, as personsof ordinary skill in the art will understand.

Magnet 112 is arranged with magnet caps 215A, 215B, and 215C. In theembodiment shown, magnet 112 is attached to magnet cap 215B, which isdisposed against or in contact with magnet caps 215A and 215C. A varietyof types and shapes of magnets may be used, as desired. As noted,examples include neodymium-iron-boron (NIB) or aluminum nickel cobalt(ALNICO) alloy magnets, but other materials, such as alloys withappropriate properties, may be used. In some embodiments, magnet 112 mayextend to a cavity in bobbin 220 (described below). Other arrangementsof the magnet and magnet caps or support are possible and contemplated,as persons of ordinary skill in the art will understand.

Coil 109 is wound on a bobbin 220. In the embodiment shown, coil 109 andbobbin 220 together form the proof mass (neglecting the mass of spring106). In the embodiment shown, coil 109 is wound around bobbin 220,although other arrangements are possible and contemplated, as persons ofordinary skill in the art will understand.

The proof mass is suspended by spring 106, which for illustrationpurposes is shown as four sections labeled 106A-106D. In exemplaryembodiments, spring 106 may include one, two, or more springs, such asflat, leaf, or spider springs, as desired. Other types and/orarrangements of spring 106 are possible and contemplated, as persons ofordinary skill in the art will understand. As noted above, a variety ofmaterials and techniques may be used to fabricate spring 106. Someexamples include etching or die cutting. Beryllium copper may be used asone example of spring material, but other materials with appropriatespring properties (e.g., having relatively low temperature coefficient)may be used, as desired.

In exemplary embodiments, such as the embodiment of FIG. 7, spring 106may have a relatively low spring constant. More specifically, spring 106may have sufficient stiffness to suspend and support the proof mass. Asnoted above, a virtual spring (not shown), having a relatively highspring constant (i.e., higher than the spring constant of spring 106)operates in conjunction with spring 106. Thus, spring 106 may providejust enough stiffness to physically support the proof mass.

In the embodiment shown in FIG. 7, spring 106 (shown as sections orportions 106A-106D) suspend the proof mass with respect to magnet 112(and magnet caps 215A-215C, if used). In other words, a stimulus, suchas force, applied to sensor 250 causes the proof mass to move orexperience a displacement with respect to magnet 112 (and magnet caps215A-215C). Other arrangements are possible and contemplated, as personsof ordinary skill in the art will understand. For example, spring 106may attach to magnet caps 215A and 215C, rather than housing 205.

Sensor 250 includes an optical interferometer to generate an electricalsignal in response to displacement of coil 109 in relation to magnet 112or housing 205. The electrical signal constitutes the output of theoptical interferometer. The electrical signal may be provided to anamplifier, e.g., TIA 118 in FIG. 3.

Referring again to FIG. 7, in the embodiment shown, the opticalinterferometer includes a light source 225, such as a VCSEL. The lightoutput of light source 225 is reflected by a mirror 222, and isdiffracted by diffraction grating 235. The resulting optical signals aredetected by optical detectors 230A, 230B, and 230C.

A stimulus applied to sensor 250 causes a change in the detected light,and thus causes optical detectors 230A-230C to provide an electricaloutput signal. The electrical output signal, e.g., a current signal, maybe used in a feedback loop, as discussed above.

Note that, if desired, the electrical output signal may be used in anopen-loop configuration, rather than in a closed-loop (negativefeedback) configuration. As noted above, closed-loop configurationprovides some advantages over open-loop configuration. In somesituations, however, operating sensor 250 in an open-loop configurationmay be desired, for instance, on a temporary basis.

FIG. 8 shows a schematic diagram or circuit arrangement 300A for asensor according to an exemplary embodiment, for instance sensors 200and 250 in FIGS. 6 and 7, respectively. Referring to FIG. 8, asdescribed above, optical detectors 230A-230C (photodiodes in theembodiment shown) provide an output signal to TIA 118. A bias source,labeled V_(BIAS), for example, ground or zero potential, provides anappropriate bias signal to detectors 230A-230C. In the embodiment ofFIG. 8, the output signal of optical detectors 230A-230C is provided toTIA 118 as a differential signal.

Note that FIG. 8 omits light source 225 for the sake of clarity ofpresentation. Light source 225, e.g., a VCSEL, may be powered by anappropriate circuit (not shown). Examples include a voltage regulator, areference source, etc., as desired. Also, in some embodiments, MCU 310may control or program the light level that light source 225 emits,depending on various factors, such as power consumption, desired sensorparameters and performance, etc.

In the embodiment shown in FIG. 8, TIA 118 includes two individual TIAcircuits or amplifiers, 118A and 118B, to accommodate the differentialinput signal. TIA 118 includes resistors 305A-305B to adjust (orcalibrate or set or program or configure) the gain of TIAs 118A-118B,respectively.

Thus, by adjusting resistor 305A, the gain of amplifier 118A may beadjusted. Similarly, by adjusting resistor 305B, the gain of amplifier118B may be adjusted. A controller, such as a microcontroller unit (MCU)310 in the exemplary embodiment shown, adjusts the values of resistors305A-305B.

Typically, given the differential nature of the input signal of TIA 118,MCU 310 adjusts resistors 305A-305B to the same resistance value so asto increase or improve the common-mode rejection ration (CMRR) of TIA118. Put another way, the two branches of TIA 118, i.e., the branchescontaining amplifiers 118A and 118B, respectively, are typically matchedby adjusting resistors 305A-305B to the same resistance value. In somesituations, however, resistors 305A-305B might be adjusted to differentvalues, for example to compensate for component mismatch, manufacturingvariations, etc.

Note that adjusting the gains of amplifiers 118A-118B does not set thefull-scale range of the sensor. Rather, the gains of amplifiers118A-118B determine the overload point of the sensor, i.e., the peakoverload point of the sensor in response to a stimulus. Furthermore, thecoil constant of coil 109 determines the magnitude of the output signalof the sensor in response to a given amount of acceleration in responseto a stimulus, such as force. The coil constant is defined in units ofNewtons per Ampere. Increasing the coil constant increases thefull-scale range of the sensor for a given available or applied coilcurrent. For fixed values of resistors 320A and 320B, the effect ofincreasing coil constant is a decrease in the sensor's scale factor interms of Volts per unit of stimulus (e.g., acceleration (g)), asforce-balance equilibrium will be reached at a lower coil current (andhence output voltage) for a given stimulus value.

The output of amplifier 118A feeds one end or terminal of coil 109 viaresistors 315A and 320A. Conversely, the output of amplifier 118B feedsthe other end of coil 109 via resistors 315B and 320B. Thus, amplifiers118A-118B provide a drive signal for coil 109 via resistors 315A-315Band 320A-320B.

MCU 310 may adjust (or calibrate or set or program or configure) thevalues of resistors 320A-320B. Similar to resistors 305A-305B,typically, given the differential nature of the output signal of thesensor, MCU 310 adjusts resistors 320A-320B to the same resistancevalue. In some situations, however, resistors 320A-320B might beadjusted to different values, for example to compensate for componentmismatch, manufacturing variations, etc.

Note that the values of resistors 320A-320B affect the gain or scalefactor of the sensor. In other words, the values of resistors 320A-320Bdetermine the full range or scale that the sensor can sense, e.g., thefull range of acceleration in response to the stimulus.

Nodes 325A and 325B provide the differential output signal of thesensor. In the embodiment shown, node 325A provides the positive outputsignal, whereas node 325B provides the negative output signal. Together,the positive and negative output signals provide a differential outputsignal that is proportional to acceleration, a, experienced by the proofmass in response to the stimulus (e.g., force), as discussed above.

In some embodiments, MCU 310 may include circuitry to receive andprocess the output signal provided at nodes 325A-325B. For example, MCU310 may include analog-to-digital converter (ADC) circuitry to convertthe output signal at nodes 325A-325B to a digital quantity. MCU 310 maycommunicate the resulting digital quantity to another circuit orcomponent, for example, via link 370, as desired. Furthermore, MCU 310may receive power (to supply the various components in the sensor) orother information, for example, parameters related to adjusting variousresistor values, as described above, via link 370.

FIG. 9 shows a schematic diagram or circuit arrangement 300B for asensor according to an exemplary embodiment, for instance sensors 200and 250 in FIGS. 6 and 7, respectively. Referring to FIG. 9, asdescribed above, optical detectors 230A-230C (photodiodes in theembodiment shown) provide an output signal to TIA 118. In the exampleshown, V_(BIAS) is ground potential although, as noted above, otherappropriate values may be used. In the embodiment of FIG. 9, the outputsignal of optical detectors 230A-230C is provided to TIA 118 as asingle-ended signal.

Note that FIG. 9 omits light source 225 for the sake of clarity ofpresentation. Light source 225, e.g., a VCSEL, may be powered by anappropriate circuit (not shown). Examples include a voltage regulator, areference source, etc., as desired. Also, in some embodiments, MCU 310may control or program the light level that light source 225 emits,depending on various factors, such as power consumption, desired sensorparameters and performance, etc.

The gain of TIA 118 may be adjusted by adjusting (or calibrating orsetting or programming or configuring) resistor 305. In the embodimentshown, MCU 310 adjusts the values of resistor 305. In other embodiments,other arrangements may be used, as desired, for example, use of a hostor controller coupled to the sensor, described below.

The output of TIA 118 drives an input of amplifier 345 via resistor 335.A feedback resistor 340 couples the output of amplifier 345 to resistor335 (input of amplifier 345). If desired, the gain of amplifier 345 maybe adjusted by adjusting resistor 340 (more specifically, the ratio ofresistors 340 and 335). In the embodiment shown, MCU 310 may adjust thevalue of resistor 345.

The output of amplifier 345 drives an input of amplifier 355 viaresistor 350. A feedback resistor 360 couples the output of amplifier355 to resistor 350 (input of amplifier 355). If desired, the gain ofamplifier 355 may be adjusted by adjusting resistor 360 (morespecifically, the ratio of resistors 360 and 350). In the embodimentshown, MCU 310 may adjust the value of resistor 360.

Note that adjusting the gain of TIA 118 (and optionally the gains ofamplifiers 345 and 355) does not set the full-scale range of the sensor.Rather, the gain of TIA 118 (and optionally the gains of amplifiers 345and 355) determines the overload point of the sensor, i.e., the peakoverload point of the sensor in response to a stimulus. Furthermore, thecoil constant of coil 109 determines the magnitude of the output signalof the sensor in response to a given amount of acceleration in responseto a stimulus, such as force. More specifically, the coil constant ofcoil 109 in conjunction with the values of 320A and 320B determine theoutput scale factor in Volts per unit of stimulus, e.g., g ofacceleration.

The output of amplifier 345 feeds one end or terminal of coil 109 viaresistors 315A and 320A. Conversely, the output of amplifier 355 feedsthe other end of coil 109 via resistors 315B and 320B. Thus, amplifiers345 and 355 provide a drive signal for coil 109 via resistors 315A-315Band 320A-320B.

MCU 310 may adjust (or calibrate or set or program or configure) thevalues of resistors 320A-320B. Note that the values of resistors320A-320B affect the gain or scale factor of the sensor. In other words,the values of resistors 320A-320B determine the full range or scale thatthe sensor can sense, e.g., the full range of acceleration in responseto the stimulus.

Nodes 325A and 325B provide the differential output signal of thesensor. In the embodiment shown, node 325A provides the positive outputsignal, whereas node 325B provides the negative output signal. Together,the positive and negative output signals provide a differential outputsignal that is proportional to acceleration, a, experienced by the proofmass in response to the stimulus (e.g., force), as discussed above.

In some embodiments, MCU 310 may include circuitry to receive andprocess the output signal provided at nodes 325A-325B. For example, MCU310 may include analog-to-digital converter (ADC) circuitry to convertthe output signal at nodes 325A-325B to a digital quantity. MCU 310 maycommunicate the resulting digital quantity to another circuit orcomponent, for example, via link 370, as desired. Furthermore, MCU 310may receive power (to supply the various components in the sensor) orother information, for example, parameters related to adjusting variousresistor values, as described above, via link 370.

Note that although the exemplary embodiments of FIGS. 8-9 show MCU 310as the controller, other possibilities exist and are contemplated. Forexample, a processor (e.g., a central processing unit (CPU) or othertype of processor), a logic circuit, a finite-state machine, etc., maybe used to control the values of the various resistors. The choice ofthe controller used depends on factors such as design and performancespecifications, the degree of flexibility and programmability desired,the available technology, cost, etc., as persons of ordinary skill inthe art will understand.

FIG. 10 illustrates the output signal 400 of a TIA 118 in an exemplaryembodiment, for example, one of the embodiments of FIGS. 3 and 6-9.Output signal 400 shows how the output signal 400 (measured in Volts) ofTIA 118 varies as a function of displacement, x (measured in meters).The output signal 400 shows a variation around a reference point 405 inresponse to displacement.

Thus, in the example shown, in response to a displacement x₁, having,for example, an absolute value of 100 nm around reference point 405(say, ±100 nm), the output signal 400 varies from −V to +V, for example,by ±2 volts. The output signal 400 is a function of the gain of TIA 118.As noted above, the gain of TIA 118 determines the peak response oroverload point of TIA 118.

Note that the output signal 400 of TIA 118 may be periodic (e.g., acyclical interference fringe condition) in response to displacement, aspersons of ordinary skill in the art will understand. FIG. 10 showsmerely a portion of output signal 400 for the sake of discussion.

FIG. 11 shows a flow diagram 500 for a method of operating a sensoraccording to an exemplary embodiment. More specifically, the figureillustrates the actions that a controller, such as MCU 310, describedabove, may take, starting with the sensor's power-up.

After power-up, at 505 MCU 310 is reset. The reset of MCU 310 may beaccomplished in a variety of ways. For example, a resistor-capacitorcombination may hold the reset input of MCU 310 for a sufficiently longtime to reset MCU 310. As another example, a power-on reset circuitexternal to MCU 310 may cause MCU 310 to reset. As another example, MCU310 may be reset according to commands or control signals from a host.

After reset, MCU 310 begins executing firmware or user programinstructions. The firmware or user program instructions may be includedin a storage circuit within MCU 310 (e.g., internal flash memory) or ina storage circuit external to MCU 310 (e.g., an external flash memory).In any event, MCU 310 takes various actions in response to the firmwareor user program instructions.

At 510, MCU 310 adjusts one or more resistors (e.g., resistors 305A-305Bin FIG. 8 or resistor 305 in FIG. 9) to calibrate the gain of TIA 118(see, for example, FIGS. 8 and 9). As described above in detail, thegain of TIA 118 affects certain attributes of the sensor.

At 515, MCU 310 adjusts resistors (e.g., resistors 320A-320B in FIGS. 8and 9) in the signal path that drives coil 109 (see, for example, FIGS.8 and 9). As described above in detail, the values of resistors320A-320B affects certain attributes of the sensor, such as gain orscale of the sensor. Optionally, MCU 310 may make other adjustments orcalibrations, for example, it may adjust the values of resistors 340 and360 (see FIG. 9).

Referring again to FIG. 11, at 520 MCU 310 may optionally enter a sleepstate. In the sleep state certain parts or blocks of MCU 310 may bedisabled or powered down or placed in a low-power state (compared towhen MCU 310 is powered up). Examples include placing the processor,input/output (I/O) circuits, signal processing circuits (e.g., ADC),and/or other circuits (e.g., arithmetic processing circuits) of MCU 310in a sleep state.

Placing some of the circuitry of MCU 310 in a sleep state lowers thepower consumption of MCU 310, in particular, and of the sensor, overall.Depending on the amount of power consumed in the sleep state and factorssuch as power-source capacity (e.g., the capacity of a battery used topower the sensor), MCU 310 may remain in the sleep state for relativelylong periods of time, e.g., days, weeks, months, or even longer. Thus,the power savings because of the use of the sleep state provide aparticular benefit in portable or remote applications where a batterymay be used to power the sensor.

Note that some circuitry in MCU 310 may be kept powered up, even duringthe sleep mode or state. For example, a real-time clock (RTC) circuit(or other timer circuitry) may be kept powered and operational so as totrack the passage of time. As another example, interrupt circuitry ofMCU 310 may be kept powered and operation so that MCU 310 may respond tointerrupts.

As part of entering the sleep state, the state of MCU 310 may be saved,for example, contents of registers, content of the program counter, etc.Saving the state of MCU 310 allows restoring MCU 310 later (e.g., whenMCU 310 wakes up or resumes from the sleep state) to the same state aswhen it entered the sleep state.

MCU 310 may leave the sleep mode or state (wake up) and enter the normalmode of operation (e.g., processing signals generated in the sensor inresponse to a stimulus), or resume from the sleep state. For instance,in some embodiments, MCU 310 (or a CPU or other processor or controller)remains in the sleep state until one or more conditions are met, forexample, the output signal (Out+−Out−) exceeding a preset threshold orvalue, or a timer generating a signal after a preset amount of time haselapsed, etc. In some embodiments, once the condition(s) is/are met, aninterrupt may be generated to cause MCU 310 to leave the sleep state.

As part of the process of leaving the sleep state and entering thenormal mode of operation, the state of MCU 310 may be restored (if thestate was saved, as described above). Once MCU 310 leaves the sleepstate, it can process signals generated in response to the stimuli, asdescribed above.

In some embodiments, the sensor may be self-contained. In other words,the sensor, e.g., MCU 310, may include instructions for code thatdetermine how the sensor responds to stimuli, how it processes thesignals generated as a result of the application of the stimulus (e.g.,log the signal values, and time/date information, as desired), etc. Thesensor may also include a source of energy, such as a battery, to supplypower to the various circuits of the sensor. Such embodiments may besuitable for operation in conditions where access to the sensor islimited or relatively difficult.

In other embodiments, the sensor may communicate with another device,component, system, or circuit, such as a host. FIG. 12 illustrates suchan arrangement according to an exemplary embodiment.

Specifically, a sensor, such as the sensors depicted in FIGS. 3 and 6-9,includes a controller, such as MCU 310. Circuit arrangement 600 in FIG.12 also includes a host (or device or component or system or circuit)605. The sensor, specifically, the controller (MCU 310) communicateswith host 605 via link 370.

In exemplary embodiments, link 370 may include a number of conductors,and facilitate performing a number of functions. In some embodiments,link 370 may constitute a multi-conductor cable or other or similarmeans of coupling. In some embodiments, link 370 may constitute a bus.

In some embodiments, link 370 may constitute a wireless link (e.g., thesensor and host 605 include receiver, transmitter, or transceivercircuitry that allow wireless communication via link 370 by usingradio-frequency (RF) signals). Use of a wireless link provides theadvantage of communication without using cumbersome electricalconnections, and may allow arbitrary or desired locations for the sensorand host 605.

In some embodiments, link 370 may constitute an optical link. Use of anoptical link allows for relatively low noise in link 370. In such asituation, the sensor and host 605 may include optical sources and/orreceivers or detectors, depending on whether unidirectional orbidirectional communication is desired.

In some embodiments, link 370 provides a mechanism for supplying powerto various parts of the sensor. The sensor may include one or more localregulators, as desired, to regulate or convert the power received fromhost 605 (or other source), for example, by changing the voltage levelor increasing the load regulation, as desired.

In some embodiments, link 370 provides a mechanism for the sensor andhost 605 to communicate a variety of signals. Examples include datasignals, control signals, status signals, and handshaking signals (e.g.,as used in information exchange protocols). As an example, link 370provides a flexible mechanism by which the sensor may receiveinformation (e.g., calibration information) from host 605.

As another example, the sensor may provide information, such as datacorresponding to or derived from a stimulus applied to the sensors.Examples of such data include information regarding displacement,velocity, and/or acceleration. Using this mechanism, host 605 may recorda log of the data using desired intervals.

In exemplary embodiments, link 370 provides a flexible communicationchannel by supporting a variety of types of signals, as desired. Forexample, in some embodiments, link 370 may be used to communicate analogsignals. In other embodiments, link 370 may be used to communicatedigital signals. In yet other embodiments, link 370 may be used tocommunicate mixed-signal information (both analog and digital signals).

In some embodiments, host 605 may constitute or comprise an MCU (orother processor or controller) (not shown). In such scenarios, MCU 310in the sensor may be omitted or may be moved to host 605, as desired. Asan alternative, in some embodiments, the MCU in host 605 may communicatewith MCU 310 in the sensor.

One aspect of the disclosure relates to sensors with programmable gainand dynamic range/dynamic range compression. As noted above, typicallythe output signal of a sensor according to an exemplary embodiment (see,for example, FIGS. 8-9), is provided to follow-on circuitry for furthersignal processing, such as to an ADC, an amplifier, etc. (whetherincluded in MCU 310, discrete circuitry, or other arrangement).

Typically, the dynamic range of the sensor exceeds that of the follow-oncircuitry. Put another way, the follow-on circuitry typically has morenoise than does the sensor, which limits the dynamic range of theoverall circuit. In exemplary embodiments, a nonlinear transfer functionmay be used to modify the dynamic range of the sensor, and match thesensor's dynamic range to the dynamic range of the follow-on circuitry.

The nonlinear transfer function may be added to sensors according tovarious embodiments in a number of ways. In some embodiments, thenonlinear transfer function may be implanted by modifying the feedbacknetwork or circuit of the sensor, such as the circuitry around TIA 118or other circuitry, such as amplifier 345 or amplifier 355 (see FIGS. 8,9). In some embodiments, TIA 118 and/or other circuitry, such asamplifier 345 and/or amplifier 355, may be modified to have alogarithmic response, as desired.

In other embodiments, the nonlinear transfer function may be implementedby adding a circuit, a feedback network, in the negative feedback loopor circuit that includes TIA 118 and coil 109. For example, a feedbacknetwork or circuit with a nonlinear transfer function may be added atthe output of TIA 118, the output of amplifier 345, and/or the output ofamplifier 355. An example of such a circuit includes a logarithmicamplifier or circuit.

FIG. 13 depicts a nonlinear transfer function 700 used to modify thedynamic range of a sensor according to an exemplary embodiment. Transferfunction 700 has a linear or nearly linear portion 703. In response toinput stimuli, the output voltage of the sensor varies linearly ornearly linearly in this portion. In other words, as the input stimulusvaries from P₁ to P₂ (approximately, because of the “soft” corner in thetransfer function), corresponding to the output levels labeled −V_(sc)(soft-clip voltage) and +V_(sc), the output voltage varies linearly (ornearly linearly), with a slope m₁. (Note that for stimulus values nearP₁ and P₂, the output voltage exhibits some nonlinear behavior.)

Transfer function 700 has another linear or nearly linear portion 706.For input stimulus below P₁ or above P₂, portion 706 governs the outputvoltage. As the input stimulus goes below P₁ or above P₂(approximately), portion 706, with a slope m₂, determines the level ofthe output signal. Thus, points P₁ and P₂ constitute inflection points,at or near which the gain and dynamic range of the sensor are modifiedin a nonlinear fashion, i.e., a change from slope m₁ to slope m₂ andvice-versa, depending on the direction of change in the input stimulus.

Note that slope m₁ is larger than slope m₂. In other words, for inputstimulus levels below P₁ or above P₂ (approximately), the sensorexhibits less overall gain and smaller dynamic range than it does forstimulus levels between P₁ and P₂ (approximately). By programming (ormodifying or setting or configuring) slopes m₁ and m₂ and/or levels P₁and P₂, the gain and dynamic range (or dynamic range compression) of thesensor may be modified, for example, to desired levels orcharacteristics.

Note further that the transition from portion 703 to portion 706 (orvice-versa) of the transfer function occurs smoothly. Put another way,the first-order derivative of transfer function 700 varies continuouslyas the response of the sensor makes a transition from portion 703 toportion 706 (or vice-versa).

In some embodiments, the nonlinear transfer function may have apiecewise-linear shape. FIG. 14 shows a transfer function 720 with apiecewise-linear (nonlinear, overall) characteristic. Transfer function720 has a linear or nearly linear portion 723. In response to inputstimuli, the output voltage of the sensor varies linearly or nearlylinearly in this portion. In other words, as the input stimulus variesfrom P₁ to P₂, corresponding to the output levels labeled −V_(sc)(soft-clip voltage) and +V_(sc), the output voltage varies linearly (ornearly linearly), with a slope m₁.

Transfer function 720 has another linear or nearly linear portion 726.For input stimulus below P₁ or above P₂, portion 726 governs the outputvoltage. As the input stimulus goes below P₁ or above P₂, portion 726,with a slope m₂, determines the level of the output signal. Thus, pointsP₁ and P₂ constitute inflection points, at (or near) which the gain anddynamic range of the sensor are modified in a nonlinear fashion, i.e., achange from slope m₁ to slope m₂ and vice-versa, depending on thedirection of change in the input stimulus.

Note that slope m₁ is larger than slope m₂. In other words, for inputstimulus levels below P₁ or above P₂), the sensor exhibits less overallgain and smaller dynamic range than it does for stimulus levels betweenP₁ and P₂. By programming (or modifying or setting or configuring)slopes m₁ and m₂ and/or levels P₁ and P₂, the gain and dynamic range (ordynamic range compression) of the sensor may be modified, for example,to desired levels or characteristics.

Note further that the transition from portion 723 to portion 726 (orvice-versa) of the transfer function occurs relatively abruptly (e.g.,compared to transfer function 700 of FIG. 13). Put another way,referring back to FIG. 14, the first-order derivative of transferfunction 720 as a discontinuity (at −V_(sc) and +V_(sc)) as the responseof the sensor makes a transition from portion 723 to portion 726 (orvice-versa).

In some embodiments, the gain and dynamic range of the sensor may beprogrammed (or modified, set, configured, etc.) to provide a family,set, or a number of profiles of characteristics. In other words, thesensor's characteristics (gain, dynamic range) may be programmed byselecting one of a number of nonlinear transfer functions (e.g.,feedback networks or circuits) to be included in the feedback network.The selected nonlinear transfer function may subsequently be changed toanother nonlinear transfer function, as desired. In this manner, sensorswith flexible, programmable properties, such as gain and dynamic rangeprofiles, may be provided.

FIG. 15 illustrates a set or family of nonlinear transfer functions730A-730C that may be used in a sensor according to an exemplaryembodiment. The set of nonlinear transfer functions shown in the figureincludes three nonlinear transfer functions, although fewer or morenonlinear transfer functions may be used, as desired. Furthermore,although piecewise-linear nonlinear transfer functions are shown in thefigure, other types of nonlinear transfer function may be used, forexample, the nonlinear transfer function shown in FIG. 13.

Referring again to FIG. 15, transfer functions 730A each have a linearor nearly linear portion 733A-733C, respectively. Similar to thenonlinear transfer function of FIG. 14, in response to input stimuli,the output voltage of the sensor varies linearly or nearly linearly inportions 733A-733C. In other words, as the input stimulus varies in arange corresponding to the output levels labeled −V_(sc) and +V_(sc),the output voltage varies linearly (or nearly linearly).

Transfer functions 730A-730C each have another linear or nearly linearportion 736A-736C, respectively. For input stimulus below or above therange that results in output voltages of −V_(sc) to +V_(sc),respectively, portions 736A-736C govern the output voltage. Similar tothe transfer function shown in FIG. 14, the two respective portions oftransfer functions 730A-730C have differing slopes, which result in thegain and dynamic range of the sensor to vary in a nonlinear fashion,i.e., according to a change from one slope level to another slope leveland vice-versa, depending on the direction of change in the inputstimulus.

Note that although FIG. 15 shows a set of piecewise-linear transferfunctions, other types or curves or functions may be used. For example,some or all of the transfer functions in FIG. 15 may be replaced withthe type of nonlinear function shown in FIG. 13, as desired.

As noted above, the nonlinear transfer functions may be implemented in avariety of ways in sensors according to exemplary embodiments. Moreparticularly, various attributes of the sensor, such as gain,sensitivity, and dynamic range, may be programmed by selecting a desirednonlinear transfer function for inclusion in the feedback path of thesensor.

Selection of nonlinear transfer function may be made by coupling oruncoupling one or more circuits, e.g., feedback networks, as part of theoverall feedback network of the sensor. FIG. 16 shows a circuitarrangement 750 that uses this scheme.

Circuit arrangement 750 includes TIA 118, switches 753A-753D coupled tofeedback networks 756A-756D. Feedback networks 756A-756D are coupled todrive coil 106, for example, via coil driver 762. Note that, dependingon the specific components and circuitry used (e.g., drive strengths),coil driver 762 may be omitted, or an amplifier in the sensor may beused to drive coil 106.

Feedback networks 756A-756D may correspond to a set of nonlineartransfer functions, such as transfer functions 730A-730C of FIG. 15.Thus, in this example, feedback networks 756A-756C provide a gain thatcorresponds to the slope of portions 733A-733C of transfer functions730A-730C.

Referring again to FIG. 16, feedback network 756D corresponds toportions 736A-736C of transfer functions 730A-730C. In portions736A-736C, the soft-clip portions, feedback network 756D provides a gainthat corresponds to a lower slope than the slope of portions 733A-733C.The slope in the soft-clip portions may be fixed or might be differentamong the transfer functions, as desired, depending on the particularcircuitry of feedback network 756D.

By selectively closing one of switches 753A-753D, the corresponding oneof feedback networks 756A-756D is coupled in the feedback loop orcircuit of the sensor. For example, closing switch 756A (while leavingswitches 756B-756D open) couples feedback network 756A in the overallfeedback loop or circuit of the sensor, and so on. Thus, the gain anddynamic range of the sensor may be programmed by selectively closingswitches 753A-753D.

Switches 753A-753D are closed depending on the output voltage of thesensor. One of switches 753A-753C is closed when the absolute value ofthe output voltage of the sensor is below V_(sc) (the output level ofsource 759). In this scenario, a gain corresponding to portions736A-736C of transfer functions 730A-730C is provided in the feedbackloop or circuit of the sensor.

Conversely, switches 753A-753C are open when the absolute value of theoutput voltage of the sensor is above V_(sc). In this situation, switch753D is closed, which causes a gain corresponding to the slope ofportions 736A-736C of transfer functions 730A-730C to be provided in thefeedback loop or circuit of the sensor. More specifically, when theabsolute value of the output voltage of the sensor is above V_(sc),diode 760 conducts, and feedback network 756D is coupled in the overallfeedback loop or circuit of the sensor. Note that in practice, anon-ideal diode has a finite forward-conduction voltage. In exemplaryembodiments, the conduction voltage of diode 760 is taken into accountwhen setting the value of V_(sc).

Referring to FIG. 16, in some embodiments, MCU 310 may be used tocontrol switches 753A-753D. By programming MCU 310, one may select thedesired transfer function for the feedback loop or circuit of thesensor. More specifically, MCU 310 may be programmed to close one ofswitches 756A-756C or switch 756D, depending on the level of the outputvoltage of the sensor, as described above. MCU 310 may do so bycomparing the output voltage of the sensor with a value corresponding toV_(sc), and providing appropriate signals to switches 753A-753D.

Note that other arrangements and alternatives are contemplated, forexample, using a remote host (see FIG. 12) to control switches753A-753D. As another example, a controller in the sensor may be used tocontrol switches 753A-753D, for example, by comparing the output voltageof the sensor with a value corresponding to V_(sc), and providingappropriate signals to switches 753A-753D.

Note that although FIG. 16 shows separate blocks for feedback networks756A-756D, in some embodiments, one or more components in a circuit maybe varied to provide a feedback network with programmablecharacteristics. For example, one or more resistors in the feedbacknetwork may be programmed (e.g., varied or modified or set) to implementa desired transfer function in the feedback loop or circuit of thesensor. As another example, by virtue of using diode 760, describedabove, a soft-clip function is provided where the scale factor of thesensor is instantaneously (or nearly instantaneously) reduced when theabsolute value of the output voltage of the sensor exceeds V_(sc).

FIG. 17 depicts a circuit arrangement 770 that may be used forprogramming a feedback network of a sensor according to an exemplaryembodiment. More specifically, circuit arrangement provides a mechanismfor programming the value of a resistor 773, which may be resistor 320A,resistor 320B, resistor 305A, resistor 305B, resistor 305, resistor 340,and or resistor 360 (see FIGS. 8-9) and, consequently, the gain orfull-scale range of the sensor. Thus, by varying or programming theresistance of one or more resistors in the feedback circuit of thesensor, such as the sensors in FIGS. 8-9, attributes of the sensor, suchas gain, sensitivity, and dynamic range may be programmed.

Referring to FIG. 17, resistor 773 includes a string or cascade of Nresistors or resistance sections 773A-773N, where N denotes a positiveinteger larger than unity. Circuit arrangement 770 includes a set of Nswitches 780A-780N, with the switches coupled across a correspondingresistor in the set of N resistors 773A-773N.

When a switch in the set of switches 780A-780N is open, thecorresponding resistor in the set of resistors 773A-773N is included inthe overall value of resistor 773. Conversely, when a switch in the setof switches 780A-780N is closed, it effectively shorts the correspondingresistor in the set of resistors 773A-773N. Thus, the correspondingresistor in the set of resistors 773A-773N is excluded from the overallvalue of resistor 773.

In other words, by selectively closing switches 780A-780N, a desiredresistance value for resistor 773 may be programmed. As a result, acorresponding gain is provided in the feedback loop or circuit of thesensor.

FIG. 18 shows a circuit arrangement 820 that may be used for programminga feedback network of a sensor according to an exemplary embodiments.Similar to resistor 773 in FIG. 17, resistor 773 in FIG. 18 includes astring or cascade of N resistors or resistance sections 773A-773N.Circuit arrangement 820 further includes a switch 825, coupled toresistors 773A-773N.

Switch 825 has a number of positions that are coupled to correspondingnodes or taps in resistor 773. For example, the left-most position ofswitch 825 couples to the node between resistor 773A and resistor 773B.As another example, the second left-most position of switch 825 couplesto the node between resistor 773B and resistor 773C, and so on. Theright-most position of switch 825 couples to the end of resistor 773.

The wiper (or common node or terminal) of switch 825 selectively couplesthe various positions to point B. Depending on the position of the wiperof switch 825, a corresponding number of resistors and, hence, a totalamount of resistance, is provided between points A and B. Thus, bychanging the position of the wiper of switch 825, the effectiveresistance of resistor 773 may be configured.

For example, when the wiper is at the left-most position of switch 825,resistor 773A is included in resistor 773. As another example, when thewiper is at the second left-most position of switch 825, resistors773A-773B are included in resistor 773, and so on. When the wiper is atthe right-most position of switch 825, resistors 773A-773N are includedin resistor 773, i.e., resistor 773 has maximum resistance.

Referring to FIGS. 17-18, the choice of the number of switches780A-780N, number of positions of switch 825, and the number ofresistors, i.e., N, affects the granularity with which the value ofresistor 773 may be programmed. A tradeoff exists between that level ofgranularity and the complexity of the circuit. The appropriate number ofswitches/switch positions and resistors depends on factors such asdesired performance specifications (e.g., the number of gain profiles),cost, complexity, space constraints, etc., as persons of ordinary skillin the art will understand.

In some embodiments, the resistance of resistors 773A-773N is equal ornearly equal, say, R ohms. In this situation, opening or closing one ofswitches 780A-780N or changing the wiper position of switch 825 changesthe value of resistor 773 by R, i.e., uniform resistance-change steps.In other embodiments, different resistance values may be used forresistors 773A-773N. By using unequal resistance values, non-uniformresistance-change steps may be implemented, for instance in situationswhere relatively large changes in gain are desired.

In the embodiment shown, MCU 310 controls switches 780A-780N or switch825. Other arrangements, however, are contemplated and may be used. Forexample, a controller, either in the sensor or in a remote location(e.g., a remote host) may control switches 780A-780N or switch 825. Asanother example, the switches may be manually controlled by a user,e.g., by setting each switch to the desired position.

As another example, switches 780A-780N or switch 825 may be controlledby a memory. More specifically, bits (or bytes, etc.) in the memory maycontrol corresponding switches 780A-780N or the wiper position of switch825. For instance, a bit with a logic high stored in it might cause oneof switches 780A-780N to turn on, whereas a bit with a logic low storedin it might cause one of switches 780A-780N to turn off.

In such a scheme, a variety of types and configurations of memory may beused. For example, a random access memory (RAM) or other type ofvolatile memory may be used in situations where the sensor's userdesires the programming of the gain to remain valid (be in effect) whilethe memory is powered on. As another example, a non-volatile memory,such as read-only memory (ROM), electrically erasable programmable ROM(EEPROM), or flash memory, may be used where the programming of the gainis to remain valid or in effect even after the memory and/or sensor arepowered off or put into the sleep state.

Switches 780A-780N may be implemented in a variety of ways, as desired,and as persons of ordinary skill in the art will understand. In someembodiments, switches 780A-780N may be implemented using transistors,such as metal oxide semiconductor (MOS) transistors. In otherembodiments, switches 780A-780N may be implemented using analogtransmission gates. In yet other embodiments, switches 780A-780N may beimplemented using manually controlled switches, relays (e.g., reedrelays), etc., as desired. Similarly, switch 825 may be implementedelectronically, mechanically, or a combination of the two.

Although sensors according to exemplary embodiments have been describedand illustrated in the accompanying drawings, a variety of otherembodiments and arrangements are contemplated. By way of illustration,the following description provides some examples.

In some embodiments, MCU 310 may be omitted. Instead, a remote host,device, component, system, circuit, etc., may couple to circuitry in thesensor to perform various operations, e.g., adjust the values of thevarious resistors. The sensor may include circuitry to facilitatecommunication with the remote host. Analog, digital, or mixed-signalcontrol communication signals may be used to adjust the resistor values,as desired.

In some embodiments, the electrical components (e.g., MCU 310, TIA 118,etc.) and rest of the sensor components (e.g., coil, optical positionsensor) reside in the same housing. In other embodiments, the electricalcomponents and rest of the sensor components reside in differentcomponents (e.g., to allow easier access to some components, whileprotecting other components) of the same housing.

In yet other embodiments, the electrical components and rest of thesensor components, for example, the coil and/or optical position sensor,reside in different or separate housings. The choice of configurationdepends on a variety of factors, as persons of ordinary skill in the artwill understand. Examples of such factors include design and performancespecifications, the intended physical environment of the sensor, thelevel of access desired to various components, cost, complexity, etc.

Sensors according to exemplary embodiments may be used in a variety ofapplications. For example, sensors according to some embodiments may beused for geological exploration. As another example, sensors accordingto some embodiments may be used for detecting seismic movement, i.e., inseismology. As another example, sensors according to some embodimentsmay be used for detecting and/or deriving various quantities related tonavigation, i.e., in inertial navigations. Other applications includeusing the sensor as a reference sensor for motion stimulus testing ofother components or sensors under test.

Referring to the figures, persons of ordinary skill in the art will notethat the various blocks shown might depict mainly the conceptualfunctions and signal flow. The actual circuit implementation might ormight not contain separately identifiable hardware for the variousfunctional blocks and might or might not use the particular circuitryshown. For example, one may combine the functionality of various blocksinto one circuit block, as desired. Furthermore, one may realize thefunctionality of a single block in several circuit blocks, as desired.The choice of circuit implementation depends on various factors, such asparticular design and performance specifications for a givenimplementation. Other modifications and alternative embodiments inaddition to those described here will be apparent to persons of ordinaryskill in the art. Accordingly, this description teaches those skilled inthe art the manner of carrying out the disclosed concepts, and is to beconstrued as illustrative only. Where applicable, the figures might ormight not be drawn to scale, as persons of ordinary skill in the artwill understand.

The forms and embodiments shown and described should be taken asillustrative embodiments. Persons skilled in the art may make variouschanges in the shape, size and arrangement of parts without departingfrom the scope of the disclosed concepts in this document. For example,persons skilled in the art may substitute equivalent elements for theelements illustrated and described here. Moreover, persons skilled inthe art may use certain features of the disclosed concepts independentlyof the use of other features, without departing from the scope of thedisclosed concepts.

1. An apparatus, comprising: a coil suspended in a magnetic field; anoptical detector to detect displacement of the coil in response to astimulus; and a feedback circuit to program a gain of the sensor,wherein the feedback circuit is coupled to the optical detector and tothe coil.
 2. The apparatus according to claim 1, wherein the feedbackcircuit varies the gain of the sensor in response to an output signal ofthe sensor.
 3. The apparatus according to claim 1, wherein the feedbackcircuit includes a feedback network with a nonlinear transfer function.4. The apparatus according to claim 2, wherein the nonlinear transferfunction comprises a piecewise-linear transfer function.
 5. Theapparatus according to claim 4, wherein the piecewise-linear transferfunction comprises a first linear portion having a first slopecorresponding to a first gain value, and a second linear portion havinga second slope corresponding to a second gain value, wherein the firstslope is larger than the second slope.
 6. The apparatus according toclaim 5, wherein the gain of the sensor is varied by using the firstgain or the second gain depending on an output signal of the sensor. 7.The apparatus according to claim 1, wherein the feedback circuitincludes a plurality of feedback networks with a corresponding pluralityof nonlinear transfer functions, and wherein the gain of the sensor isprogrammed by selecting a feedback network from the plurality offeedback networks.
 8. The apparatus according to claim 7, wherein atleast one of the plurality of nonlinear transfer functions comprises apiecewise-linear transfer function.
 9. The apparatus according to claim7, wherein the feedback circuit varies the gain of the sensor inresponse to an output signal of the sensor.
 10. The apparatus accordingto claim 1, wherein the gain of the sensor is programmed by changing aresistance of at least one resistor in the feedback circuit.
 11. Amethod of operating a sensor that includes a coil suspended in amagnetic field and an optical detector to detect displacement of thecoil in response to a stimulus, the method comprising programming a gainof the sensor by using a feedback circuit that is coupled to the opticaldetector and to the coil.
 12. The method according to claim 11, whereinprogramming a gain of the sensor further comprises varying the gain ofthe sensor in response to an output signal of the sensor.
 13. The methodaccording to claim 11, wherein the feedback circuit includes a feedbacknetwork with a nonlinear transfer function.
 14. The method according toclaim 13, wherein the nonlinear transfer function comprises apiecewise-linear transfer function.
 15. The method according to claim14, wherein the piecewise-linear transfer function comprises a firstlinear portion having a first slope corresponding to a first gain value,and a second linear portion having a second slope corresponding to asecond gain value, wherein the first slope is larger than the secondslope.
 16. The method according to claim 11, wherein programming thegain of the sensor further comprises using the first gain or the secondgain depending on an output signal of the sensor.
 17. A sensor,comprising: a magnet, having an associated magnetic field; a coilsuspended by a spring in the magnetic field of the magnet; an opticaldetector to detect displacement of the coil in response to a stimulusapplied to the sensor; and a feedback circuit coupled to the opticaldetector and to the coil, the feedback circuit to program a gain of thesensor by using at least one nonlinear transfer function.
 18. The sensoraccording to claim 17, wherein the stimulus comprises acceleration. 19.The sensor according to claim 17, wherein the at least one nonlineartransfer function comprises a piecewise-linear transfer functioncomprising a first linear portion having a first slope corresponding toa first sensor gain, and a second linear portion having a second slopecorresponding to a second sensor gain, wherein the first sensor gain islarger than the second sensor gain.
 20. The sensor according to claim17, wherein depending on an output signal of the sensor amicrocontroller unit (MCU) programs the gain of the sensor by causingthe feedback circuit to use the first linear portion or the secondlinear portion of the at least one nonlinear transfer function.